reserve E, x, y, X for set;
reserve A, B, C for Subset of E^omega;
reserve a, a1, a2, b for Element of E^omega;
reserve i, k, l, m, n for Nat;

theorem
  A+ ^^ (A?) = A+
proof
  thus A+ ^^ (A?) = A |^.. 1 ^^ (A?) by Th50
    .= A |^.. 1 by Th41
    .= A+ by Th50;
end;
